Under TREE_PREEMPT_RCU, print_other_cpu_stall() invokesrcu_print_task_stall() with the root rcu_node structure's ->lockheld, and rcu_print_task_stall() acquires that same lock forself-deadlock. Fix this by removing the lock acquisition fromrcu_print_task_stall(), and making all callers acquire the lockinstead.